Such a circuit-breaker is usually placed between a generator of an electrical power plant and a transformer connected to a power line.
In known manner, the main contacts are heavy enough to withstand high nominal currents without overheating. They define a relatively large volume which is more difficult to put under gas pressure or under a vacuum than is a "bottle" of smaller size disposed inside said volume. Such a bottle is provided with a stationary arcing contact and a moving arcing contact which are less heavy because they withstand only the cutoff current of the circuit-breaker.
In Patent Application FR 89 13279, the moving main contact and the moving arcing contact extend in the same longitudinal direction, so they are moved in translation parallel to that direction, by pneumatic piston-and-cylinder means.
Such means have drawbacks.
Firstly, it is necessary to provide electrically-driven valves for synchronizing the movements of the pneumatic actuators of the moving main contact and of the moving arcing contact. In particular, the moving main contact must move far enough to be able to withstand a transient voltage before the moving arcing contact opens.
Secondly, at the end of the stroke of the moving arcing contact, it is possible to obtain satisfactory acceleration, enabling the circuit-breaker to be opened more effectively, only with rather sophisticated apparatus for feeding the pneumatic actuators with gas.